The present invention relates to an attachment for a dental prosthesis.
A typical conventional Dalbo attachment for a partial dental prosthesis is shown in FIGS. 9 to 11, which are a partial sectional view (FIG. 9) showing the conventional Dalbo attachment comprising a male and a female in the state that a partial dental prosthesis having the Dalbo attachment is set in a mouth of a patient, an enlarged perspective view (FIG. 10) showing the Dalbo attachment of FIG. 9 in the state that the male and the female are separated to each other, and an enlarged perspective view (FIG. 11) showing the Dalbo attachment of FIG. 9 in the state that the male and the female are engaged with each other, respectively. The Dalbo attachment is described in Etsuro Matsuo, Clinic Concerning Attachment, pages 9 to 11, published on Nov. 15, 1970 by Ishiyaku Shuppan Kabushiki Kaisha. In FIGS. 9 to 11, numeral 34 indicates a partial dental prosthesis. The partial dental prosthesis 34 has artificial teeth 35 and a denture base 36 on which the artificial teeth 35 are held. Numeral 37 indicates a retentive tooth which is a natural tooth covered with a metallic crown. Numeral 38 indicates a Dalbo attachment. The Dalbo attachment 38 has a male member 39 secured to the retentive tooth 37 by soldering and a female member 40 secured to the partial dental prosthesis 34. The male member 39 and the female member 40 are made of Au containing Pt, respectively. As shown in FIG. 10, the male member 39 has a rail 42, an arm extending from the lower end of the rail 42 perpendicular to the longitudinal axis of the rail 42 and a spherical body 43 provided at a free end of the arm. The female member 40 has a groove 41 capable of being slidably in contact with the rail 42, a hole 44 having a circular section of which diameter is smaller than that of spherical body 43 and which can be engaged with the spherical body by receiving the spherical body from lower side, slits 45 (as shown in FIG. 5) longitudinally extended along a wall defining the hole 44 and a fixing element 46 through which the female member 40 is secured to the artificial tooth 35.
In operation of the Dalbo attachment 38, the groove 41 of the female member 40 is made to be in contact with the rail 42 of the male member 39. The female member 40 is slided downwardly in the state that the groove 41 is in contact with the rail 42. Then, the spherical body 43 of the male member 39 is engaged with the circular hole 44. That is to say, the spherical body 43 is fixed into the hole 44 with the elastic gripping force (applied in the direction of a center of the hole 44) of the wall. The elastic gripping force of the female 40 is generated due to the slits 45.
In such a Dalbo attachment, there are problems, as follows:
(1) The attachment of this kind is easy to break, since the mechanical strength of the attachment constituted by precisely processing metallic material is weak. In detail, an occlusal pressure (about 60 kg/cm.sup.2) causes a large force which applies to the attachment, so that the attachment is easy to be broken. Further, once the attachment is broken, it is almost impossible to repair. In consideration of the fact that the attachment is made of expensive metal such as Au containing Pt, the repairing cost is very high.
(2) In the above described case, not only the attachment is broken, but also the retentive tooth and the artificial tooth might be broken due to the excessive occlusal pressure.
(3) The work for securing the male and the female (both of them have mm-order-size) to the retentive tooth and the artificial tooth, respectively, requires not only high technique and high skill, but also a long manufacturing time.
(4) It is insanitary to use the above described Dalbo attachment having the cutting lines, since a space is formed by the cutting lines when gripping the spherical body elstically. Therefore, the space is easily filled with dregs remaining in the mouth after eating.
(5) The force for securing the fema1e member 40 to the artificial tooth 35 is weak, since the female member is secured to the artificial tooth substantially only through the element 46.
On the other hand, a bar attachment for a dental prosthesis is well known. Such a bar attachment is described in Etsuro Matsuno, Clinic Concerning Attachment, page 30, published on Nov. 15, 1970 by Ishiyaku Shuppan Kabushiki Kaisha or Japanese unexamined patent application No. 102238/1981. The bar attachment is known as Dolder bar attachment, Ackermann bar attachment and Hader Plastik Reiter. The Dolder bar attachment for the dental prosthesis is shown in FIGS. 12 and 13, which are a partial perspective view showing a Dolder bar and a sleeve of the conventional Dolder bar attachment for a dental prosthesis in the state of engaging with each other and a partial sectional view showing the attachment in FIG. 12 in the state that the Dolder bar is engaged with the sleeve, respectively. In FIG. 12, the Dolder bar attachment comprises a bar 47 having an approximate circular section, for example, an oval section and a sleeve 48 with which the bar 47 is engaged. Numeral 49 is a space provided between the bar 47 and the sleeve 48. The space 48 has an operation to absorb a pressure applied to the attachment. The bar 47 is curved along the shape of an alveolus ridge 4. Both ends of the bar 47 are fixed to dental roots, for example, of canine teeth. The sleeve 48 is provided in a groove formed in an inner surface of the denture base 52 as shown in FIG. 13. Numerals 53, 53 indicate spaces provided between the lower outer surfaces of the sleeve 48 and the corresponding lower inner side surfaces of the groove. The spaces give an elasticity to the sleeve 48. That is to say, when the bar 47 is engaged with the sleeve 48, the sleeve 48 can be widened outwardly. Therefore, the bar 47 is elastically gripped by the force generating when the widened sleeve 48 returns to the original shape.
In such a bar attachment, there are several problems, as follows:
(1) With respect to the Dolder bar attachment or the Ackermann bar attachment, it is necessary that the spaces are provided between the lower outer surfaces of the sleeve and the correponding lower inner side surfaces of the groove in order to give an elasticity to the sleeve. However, dregs existing in the mouth are easy to come into the spaces, so that it is unsanitary to use the attachment in the mouth.
(2) The elasticity of the sleeve becomes unstable, since the sleeve is made of metal. Due to the repeated use, the force that the sleeve elastically grips the bar tends to decrease.
(3) The bar and the sleeve must be correspondingly curved with each other. However, it is very difficult that both of them are precisely formed into the corresponding shapes and are precisely located to each predetermined position. Conventionally, the forming and locating steps are performed by a manual work of the skilled person.
(4) With respect to the Hader Plastik Reiter, the strength is weak, since the sleeve is made of a plastic. Therefore, it is necessary to increase the thickness of the sleeve, but it is difficult to manufacture such a sleeve, further, it is not easy to precisely locate the sleeve to the predetermined position.
(5) With respect to the Dolder bar attachment and Ackermann bar attachment, since the space is provided between the bar and the sleeve so that these attachments have the means for absorbing pressure during a mastication movement, dregs in the mouth unsanitarily tend to come into the space.
Further, a stud attachment for a dental prosthesis is well known. The stud attachment for the dental prosthesis is shown in FIGS. 14 and 15, which are a partial sectional view showing the conventional stud attachment for the dental prosthesis in the state that a male member is engaged with a female member and a plan view showing an opened end of a female member of the attachment in FIG. 14. Such a stud attachment is described in Etsuro Matsuo, Clinic Concerning Attachment, page 29, published on Nov. 15, 1970 by Ishiyaku, Shuppan Kabushiki Kaisha or Japanese unexamined patent application No. 72911/1980. In FIG. 14 and FIG. 15, numeral 54 indicates a metallic male pin. The male pin 54 is fixed to a surface of a dental root 55 formed by cutting a corona dentis of a natural tooth. Numeral 56 indicates a metallic female member which is engaged with the male pin 54. The female member 56 is formed into a cylindrical body. The cylindrical body is closed at an end and opened at the other end. The closed end side of the cylindrical body is embedded into a hole which is provided in an inner surface of a denture base 59. Then, the closed end side of the cylindrical body is fitted on an corresponding inner peripheral surface of the hole, and the opened end side is apart from the corresponding inner peripheral surface of the hole. That is to say, there is a space between a side surface of the opened end side and the corresponding inner peripheral surface of the hole. At the opened end side of the cylindrical body, the cylindrical body has three cutting lines 57 extending from the opened end in the direction of an axis of the cylindrical body. The inner diameter of the opened end is smaller than the inner diameter of the other portion of the cylindrical body and the maximum diameter of the head portion of the male pin 54. When the male pin 54 is inserted into the female member 56, the inner diameter of the opened end of the female member 56 radially becomes large due to the cutting lines 57. When the male pin 54 is completely engaged with the female member 56, the diameter of the opened end of the female member is a little returned so that the opened end of the female member can grip the male pin.
In such a stud attachment, there are several problems, as follows:
(1) Dregs in a mouth of a patient unsanitarily come into the female member through the cutting lines longitudinally extending from the opened end of the female member, and come into the space between the opened end of female member and the inner peripheral surface of the hole.
(2) Since the female member is made of metal, the gripping force becomes unstable. Due to the repeated mastication movement, the gripping force of the female member tends to reduce.
(3) The work to manufacture such an attachment is performed by the manual work of skilled person, since the female member is made of an expensive dental material such as Au containing Pt and precise manufacturing work is required. Therefore, there are problems in cost and working efficiency.
(4) When the force applied to the dental prosthesis is a force which generated in the direction except occlusal pressure direction, for example, the holizontal direction or the direction rotating around an axis extending from the tongue side to the cheak side, the force is transmitted to the male pin and the dental root through the female member. Therefore, it is feared that the female member, the male pin and the dental tooth are damaged.
An object of the present invention is to provide an attachment for a dental prosthesis which resolve the aforementioned problems of the prior art.